Overview
PSI4 is an open-source suite designed for performing ab initio quantum chemistry calculations. Written in C++ with Python bindings (Pybind11), it supports a wide range of methods, from Hartree-Fock (HF) and Density Functional Theory (DFT) to Coupled Cluster (CC) theories, including explicitly correlated MP2-F12 and DLPNO-CCSD(T) methods. Its modular architecture facilitates integration with community projects and extensions through plugins. PSI4 uses techniques like density fitting and multi-core execution for DFT, MP2, SAPT, and coupled-cluster calculations. It is designed to be user-friendly with simple input files and automated procedures like basis set extrapolation. PSI4 is used in research, education, and industry, emphasizing performance, flexibility, and ease of use for both users and developers.